Conventionally, in a relay network using wavelength multiplexing scheme, monitoring light with a different wavelength from signal light is used to transmit wavelength information of the signal light and the like as monitoring information for monitor and control of wavelengths to be used (Patent Document 1).
FIG. 1 shows an exemplary configuration for monitor and control in such relay network. As shown in the figure, in network 100, wavelength-multiplexed signal light is transmitted from WDM device A 110 to WDM device B 130 via linear optical repeater 120. In this case, monitoring information such as power, wavelengths in use, and the number of the wavelengths for signal light is transmitted from monitor and control circuit 112 to monitor and control circuit 132 via monitor and control circuit 122 using monitoring light with a different wavelength from the signal light.
It is required to keep the light power constant on each channel at linear optical repeater 120, even if more channels are provided in network 100 and the number of in-use wavelengths for the signal light is increased, etc., in order to prevent degradation of the transmission characteristics in the network. In this case, the monitoring information of the signal light after provided with more channels is conveyed from control circuit 114 at the transmitting side through monitoring light source 116. This monitoring light is multiplexed with the signal light at multiplexer 20a, and transmitted out to optical fiber 10.
Monitor and control circuit 122 receives the monitoring light transmitted via optical fiber 10 at optical receiver 128 and obtains the monitoring information. At the same time, monitor and control circuit 122 monitors the total light power of the signal light at the output of linear optical repeater 120, and computes the average power per channel based on the number of in-use wavelengths of the signal light obtained from the monitoring information. Monitoring control circuit 122 controls the output power of linear optical repeater 120 so that the average power becomes a desired value. Accordingly, after provided with more channels, the light power on each channel can be kept constant at linear optical repeater 120.
Further, this monitoring information is transmitted to monitor and control circuit 132 through monitoring light source 126, and received by optical receiver 138. Based on the monitoring information, control circuit 134 controls the output power of an optical amplifier in WDM device B 130 so as to be a desired value. As such, the signal light is transmitted from WDM device A 110 to WDM device B 130.
However, since the monitoring light is used in such a configuration, optical components such as light sources 116, 126, multiplexers 20a, 20c, demultiplexers 20b, 20d, and optical receivers 128, 138 are required, which are costly. Particularly, in a star-type network configuration using a power splitter network, demultiplexers and optical receivers for monitoring light are required for each subscriber terminal.
FIG. 2 shows an exemplary configuration in which the configuration for monitor and control shown in FIG. 1 is applied to a star-type wavelength multiplexed network. Network 200 is composed of an optical line terminal (OLT) 210 installed at a station, an optical fiber 10 through which wavelength-multiplexed signal light and monitoring light propagate, a power splitter 30 for power-splitting the signal light and the monitoring light in the ratio of 1 to N, and N optical network units (ONUs) 230-1 to 230-N, each receiving the split signal light and the split monitoring light.
In the configuration, the monitoring information is transmitted from OLT 210 out to optical fiber 10 using monitoring light source 214. The monitoring light is split into N at power splitter 30, and transmitted to ONUs 230-1 to 230-N. Each ONU 230 receives the monitoring light with optical receiver 242, and based on in-use wavelength information transmitted as the monitoring information, tunable filter 234 and optical transmitter 238 are assigned by control circuit 244 so as to receive a predetermined channel.
However, since the monitoring light is used in this configuration, light source 214 and multiplexer 22a are required in OLT 210, and the optical components such as demultiplexer 22b and optical receiver 242 are required in each ONU, which overall cost more.
Patent Document 1: Japanese Patent Laid-Open No. 10-51057